Roots 'n' Shoots: Green Manures: Cover Crops & Green Forage

Saturday, 1 June 2013

Green Manures: Cover Crops & Green Forage

I was actually researching green forages as alternative feed for chickens when I noticed there is a large overlap between green forages and green manures. Seeing that nothing is happening in the garden for most of winter I decided to look into green manures a little bit more in detail to grow during the winter months as a cover crop. Here is what I found and thought that I should share J

Green manures, also known as cover crops, are grown as part of a good soil management and crop rotation scheme.

Sunflower flied Green manure
Helianthus annuus
Flickr upload bot
Wikipedia

Green manures fall into two main categories: Legumes (Nitrogen Fixers) and Non-legumes. The legumes add nutrients to the soil by converting atmospheric nitrogen (N2) to bio-available ammonia (NH3) in the soil. This is performed by bacteria, Rhizobia spp., that lives symbiotically with the plant contained in root nodules. Non-legumes are not able to fix nitrogen, but accomplish all the other tasks of green manures.

Green manures provide the following services:
ü    Replace or hold soil nutrients
ü    Improve soil structure (loosen hard soil, soil conditioner)
ü    Add organic material to soil
ü    Suppress weed growth
ü    Support the soil community (decomposers)
ü    Insectaries (shelter and house beneficial insects)
ü    Mulch soil & prevent wind or soil erosion
ü    Increase soil water retention
ü    Keep soil temperatures warm
ü    Flower to attract pollinating insects
ü    Some have inhibitors that prevent soil disease & pest build-up

Most vegetable gardens are dug over and the bare soil left as is for the remainder of winter. This may lead to soil and nutrient loss due to leaching and erosion. Green manures prevent this and it not like the plot is used for anything else…

Although legumes add nutrients to the soil, they are generally slow growing in autumn and provide less organic material (or biomass) than non-leguminous plants. Therefore it is preferable to use a combination of both – to get the best of both worlds J.

Some green manures have very deep reaching roots that grow into the subsoil and harvest nutrients inaccessible to other plants – for this reason they double dig.

Generally you can grow green manures in the warm or cool seasons. This means that the tilling (cutting down and working into the soil) of the summer manures occurs during autumn or winter frosts kills off the manure and winter manures are tilled before spring planting. The plants are usually tilled before flowering to prevent seed formation and the manures becoming weeds. Green manures are tilled a month before sowing any new vegetable to ensure that they have broken down and will not burn the following crop.

Lacy Phacelia
Phacelia tanacetifolium
Curtis Clark
Wikidepia

Here is a table with most of the well-known and widely used green manures (those that aren’t in the table have been provided with links below). An all-in-one resource J:

Name
Scientific Name
N2 Fixing
Winter Hardy
Season
Dig In
Chicken: Green Forage
Alfalfa
Medicago sativa
Y
Y
Winter
BF
Y
Buckwheat
Fagopyrum esculentum
N
N
Summer
BF
Y
Clover (White & Red)
Trifolium repens (W)         Trifolium pratens (R)
Y
Y
Summer (Mild winters)
AtF
Y
Fava Beans (Field, Broad beans)
Vicia faba
Y
Y
Winter
AT©
Y
Fenugreek
Trigonella foenum graecum
N
N
Summer
BF

Field Pea
Pisum sativum subsp. arvense
Y
Y
Winter
AT©
Y
Lupin (Bitter Blue)
Lupinus angustifolius
Y
Y
Summer
BF

Mustard
Sinapis alba
N
N
Winter
BF
Y
Oats
Avena sativa
N
N
Winter
BF
Y
Phacelia
Phacelia tanacetifolium
Y
Y
Winter
BF

Rye
Secale cereale
N
Y
Winter
BF
Y
Soybeans
Glycine max
Y
Y
Summer
AT©
Y
Sunflowers
Helianthus annuus
N
N
Summer
AF

Sunn Hemp
Crotalaria juncea
Y
N
Summer
BF

Trefoil (Bird’s foot)
Medicago lupulina
Y
Y
Winter
AT

Tyfon
Brassica napa
N
Y
W or S
AT
Y
Velvet Bean
Musuna puriens
Y
N
Summer
AT©

Vetch  (Hairy, tares)
Vivia sativa
Y
Y
Winter
AtF
N
Abbreviations are as following:
BF = Before flowering

AT© = Any time, can let crop

AtF = At flowering

ArF = After flowering



On that note, some of the beans and peas can be left to crop as they are easy to collect and will prevent them from going weedy. Some of the legumes are susceptible to soil borne pathogens and should not be followed by another legume crop, such a susceptible crop would be Vetch.

Sunflowers produce an allelopathic compound that suppresses weed and other plants growing nearby (good to keep in mind not to plant among other vegies!) Vetch needs to be cut at flowering for it to reach its full biomass and N2-fixing capabilities.

Alfalfa and sunflowers are drought resistant and can grow in more arid regions. Alfalfa and clover flowers attract a lot of bees! Rye and oats are easily killed by cool conditions (can easily be frost-killed), therefore winter rye and oats cultivars need to be grown in winter (those are featured in the table).

I am specifically going to mention Alfalfa, because of its green forage (alternative feed) potential for chickens. I will cover green forages for chickens in another article (see The C Files: Feed & Water). Alfalfa has a very deep rooting system and can grow to 4-9 meters tall. After the formation of its crown, it can withstand continuous grazing. It is a perennial that can live for up to 8 years and the flowers are very attractive to bees (used in bee pasturages). Alfalfa is not readily pollinated by western honey bees as the anther (structure with pollen) strikes the bee on the head when it collects honey. Bees don’t like this and learn to steal nectar from the side of the flower – thus the alfalfa leaf cutter bees are provided to pollinate alfalfa. I do not know whether this applies to African honey bees, but hopefully this will limit the seed-2-weed part. Also alfalfa seeds fail to germinate in already existing stands due to auto-toxic compounds.

Since Alfalfa is drought tolerant, can grow in the winter and provides green forage to chickens. So I decided that it should go well with my vegetable garden.

Alfalfa leafcutter bee
Megachile rotundata
Esculapio
Wikipedia


Those not covered in the article you can get full details about here:








Check out Composting for more soil conditioning tips.



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4 comments:

  1. Gosh, this is incredibly helpful, thanks! I have been putting down some green manures and this little table is very helpful for future decisions and digging in timing. I have alfalfa, clover and broad beans in at present.


    I must confess I also have learnt about cover crops! Do you know though I have always dug in my sunflowers after they flowered? Sixth sense?

    ReplyDelete
  2. We have a few alfalfa going in the garden at the moment, although I think I planted them a bit late... I haven't seen clover plants/seeds in the nurseries (also a little bit skittish of them concerning getting the correct species when you have chickens) and fava/broad beans are a recent addition (~6 months) to the shops. We are going to try favas for eating come spring as the other beans produce way to much and go hard before we get to them :)

    ReplyDelete
  3. Hi, I see this is an old post, but do you know, Livingseeds sell seeds for most of these green manures? In the pennyroyal post you mentioned you wanted to try planting red clover, which they also sell. Haven't personally started, am definitely planning to plant living mulches and green manures!

    ReplyDelete
  4. Hey hey. I am not familiar with the Livingseeds brand. The only green manure I could find at the time was Alfalfa seeds from Kirschoff but I haven't seen them in the shops for a while now... Thanx for the supplier info!

    ReplyDelete

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